The present invention relates to an optical apparatus that retains an optical element. Further, the present invention relates to an exposure apparatus that employs an optical apparatus in an optical system, which illuminates a mask with an exposure light and uses the exposure light to transfer a pattern of the mask on a substrate.
In a conventional exposure apparatus, in which an exposure light from a light source, such as an ArF excimer laser, is employed, the exposure of the exposure light to the oxygen in the air causes absorption of the exposure light by the oxygen and forms ozone. This is because the illumination spectral line of the exposure light is included in the absorption spectral line range of the oxygen. The formation of ozone may deposit a clouding substance on the surface of an optical lens and affect the characteristic of the lens in an undesirable manner. Accordingly, the space encompassing the optical path between the light source and the substrate is partially or completely covered by a cover. The interior of the cover is charged with a gas that is inert to the exposure light, such as nitrogen gas.
However, deterioration in the hermetic seal of the cover may cause ambient air, which includes impurities, to enter the cover through the deteriorated portion and deposit the above clouding substance on the optical lens surface.